The present invention is directed to high purity carbon fiber reinforced carbon composite (C/C composite) with lowering impurities content by high purity treatment. More particularly, the present invention is directed to high purity C/C composite of using high purity carbon fibers which was high purified at carbon fiber stage and manufacturing method thereof.
FIG. 2 shows a pulling single crystal apparatus used in the Czochralski process (CZ process) for manufacturing a single crystal ingot for use as a material of the semiconductor wafer and the like. As shown in FIG. 2, the CZ apparatus is so structured that a raw material in a quartz crucible 1 is heated to a high temperature by a heater 2 disposed around the quartz crucible 1 so that the raw material can be converted into the melt 3 which is pulled under vacuum pressure to form the single crystal ingot 4.
The structural elements, such as a crucible 5 supporting the quartz crucible 1 and an upper ring 6, an inner shield 7 and others which are subjected to radiant heat of the heater 2, are exposed to high temperature when pulling a single crystal ingot 4 from the quartz crucible 1 within a molten silicon. Accordingly, the structural elements must be formed of a material that can maintain a prescribed mechanical strength under high temperature. Further, the structural elements must be formed of a material of high-purity, because impurities, such as metals, contained in the structural elements become a cause of crystal defects in orientation of the solidifying of the single crystal ingot 4 and also become a factor of reduction of purity, when leaked during manufacturing. In general, a high purity graphite having excellent mechanical properties at high temperature and having high-purity is used for the structural elements of the CZ apparatus (Japanese Patent Publication No. Hei 6(1994)-35325).
Recently, with increasing diameter of the single crystal, the single crystal pulling apparatus used in the CZ process is increased in size. This produces a handling problem caused by the increased weights for the existing graphite elements and a problem of reduction in effective processing size of the inside of the apparatus.
The C/C composite has properties of lightweight and strong mechanical strength, as compared with the graphite material. By virtue of this, even when reducing in thickness, the structural elements of the C/C composite can have a strength equal to those of the graphite material, to enable an effective use of a processing chamber of the apparatus. In addition, by virtue of being lightweight, a good handling can be achieved in, for example, placement in the apparatus. By virtue of these, the crucible components used in the CZ apparatus having a large diameter are now moving from those made of the graphite to those made of the C/C composite.
However, the C/C composite was difficult to high purity for the CZ apparatus in comparison with the graphite. Then, such a problem is not only for the CZ apparatus in the semiconductor industry. An atomic energy field, aviation and universe fields have also the same problem.
In the object of the present invention to provide a high purity C/C composite with lowering contents of metal impurities with high mechanical properties at high temperature and manufacturing method thereof.
To accomplish the above the object, the high purity C/C composite formed by graphitizing a molded member packed with carbon fibers and carbon material of a matrix. The carbon fibers are high purified under halogen gas atmosphere before graphitizing. The purified carbon fibers are molded into the desired shape on a tool or in die with infiltrating the carbon material of the matrix. The molded member packed with carbon fibers and carbon material of the matrix are either independently or simultaneously graphitized with the high-purification under halogen gas atmosphere.
The carbon material of the matrix infiltrated carbon fiber become into graphite fiber after graphitizing. The carbon material of the matrix around the graphite fibers are also became into graphite and coated the graphite fibers. The inventive high-purity C/C composite consists of two graphite, namely, the high-purity graphite fibers and the high-purity graphite matrix. According to the structural of the C/C composite, the metal impurities may be difficult to dissolve from the inside of the graphite fibers.
Therefore, for example, the C/C composite was high purified under halogen gas at one time after graphitizing the molded C/C composite whose are structured to coat the graphite matrix on the graphite fibers. Accordingly the structure, the C/C composite may be mainly purified around the outside surface of the graphite matrix, and the impurities of the inside of the graphite matrix and of the graphite fibers may be difficult to purify in the purification process of these. The graphite fibers of the present invention is high purified because of the fibers are purified under halogen gas atmosphere before molding and graphitizing, and then the graphitized and the molded C/C component are either independently or simultaneously graphitized with high-purification under halogen gas atmosphere. An ash content of the C/C composite is 5 to 100 ppm, more preferably 5 to 30 ppm.
The carbon fibers may be used polyacrylonitrile (PAN), rayon or pitch. The impurities content (ash content) of the carbon fiber may be not more than 100 ppm, and more preferably 80 ppm, and more preferably 60 ppm because of the impurities content of the C/C composite is not more than 20 ppm. The carbon fibers may be high purified before or after infiltrating with the matrix.
The matrix may be used carbon including resin and/or pyrolytic carbon (PyC). The resin may be selected from the group including phenol (resole, novolak), furan, polyimide, polyamide-imide, polyether imide, polycarbodiimide and bisallyldiimide or combination thereof may be used within the range within which its property is not impaired. Solvent may be used in combination, when necessary. The material gas of the PyC may be selected from the group including aliphatic hydrocarbon as methane and propane, aromatic hydrocarbon as benzene, toluene and xylene and chlorine including hydrocarbon as dichloroethylene, dichloromethane, trichloromethane and trichloroethylene or combination thereof may be used within the range within which its property is not impaired.
The high purity C/C composite can be used for the structure member of the CZ apparatus, which manufactures bulk crystal as shown in FIG. 2. In FIG. 2, it can be used for crucible 5, upper ring 6, inner shield 7, lower ring 8, lower heater 9, thermal insulator 10 and spiltray 11. Furthermore, the high purity C/C composite can be used for the plasma confrontation the first wall of the nuclear fusion device for the atomic energy, the tile of divertor, the material for the universe aviation, and so on.